In start-up or quiescent operating conditions, integrated circuits frequently require an indication of an under-voltage condition to hold signals generated in the integrated circuit in an "off" state until the power supply input voltage is of sufficient magnitude to allow the circuit to properly operate. The under-voltage indication is typically provided by directly comparing the input voltage with an internal reference voltage, typically generated by a voltage reference device receiving a constant current. The selected output signals are maintained at the predetermined state until the particular input voltage exceeds the internal reference voltage level. However, to determine if the internally generated reference voltage itself is valid, the reference voltage will typically be compared to a second internally generated reference voltage. Alternately, the status of power supply input voltage is determined by measuring the voltage drop across the reference voltage constant current source with a comparator, wherein a lockout signal is generated when the voltage across the constant current source drops to a low value. However, integrated circuits which incorporate these methods of voltage sensing require additional voltage reference supply components, and a higher power supply input voltage to guarantee that the comparator or the second reference voltage is operable. Moreover, the operability of the primary reference voltage source is presumed from the measured voltages, which voltages may be larger than necessary to provide a reliable signal. Furthermore, lockout signals thusly generated do not provide a true indication of the point at which the voltage reference element begins to provide a regulated reference voltage.